How DNS works

To understand how does DNS (Domain Name System) work we need to take a closer look at the domain itself. Lets take some website as an example to examine closely. Let it be Education Team of Internet Engineering Task Force. Their domain name is edu.ietf.org.

All domain names should be read from right to left. In this case we see that Education Team of IETF website is located in the .ORG TLD (Top Level Domain) proposed for non-profit organizations. Next to the left the second level domain ietf - this is domain name for main IETF website. Edu is the third level domain and the domain name edu.ietf.org points directly to Education Team dedicated website.

In spite of the fact that edu.ietf.org address looks pretty sensible for human beings, machines on the network prefer to operate more machine-friendly addresses - IPs. Try to run command "ping edu.ietf.org" in the DOS box or in MacOS/Linux console. It will return the line like that: "PING edu.ietf.org (203.30.39.5) 56(84) bytes of data. " where 203.30.39.5 is IP address of Education Team of IETF's web server. It's essential to establish connection between your desktop or laptop computer and IETF's web server.

But what have happened when we ran that command or typed edu.ietf.org in the browser's location bar?

As soon as we have pressed enter our ping program (or browser) has connected to the central root server (its address is known to our software by default) and asked it about edu.ietf.org. But the root server doesn't know about edu.ietf.org's IP - it's beyond its area of responsibility. Instead of that root server has sent back to our machine IP address of another DNS server which is responsible only for .ORG top level domain. Our computer asks this DNS server about edu.ietf.org but it doesn't know it too. Instead of that it returns IP address of the DNS server who knows about all third level domains in the ietf.org zone. And this one knew the right answer.

Actually, most of the time your local computer shouldn't ask the root DNS server and all the servers below to get the right IP from a domain name. All these tasks are performed by your Internet Service Provider's DNS servers which are keeping all resolved addresses for some time. It helps to lower the load of the root server and speed up your internet connection.

When you need to setup your own web server you should setup a DNS server as well to make your third level domains (including www) resolvable. Usually it's quite easy - just follow instructions in your control panel.